Fluid streams, both liquid and gaseous, derived from natural gas reservoirs, petroleum or coal, often contain a significant amount of acid gases, for example carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), carbon disulfide (CS2), hydrogen cyanide (HCN), carbonyl sulfide (COS), or mercaptans as impurities. Said fluid streams include natural gas, refinery gas, hydrocarbon gases from shale pyrolysis, synthesis gas, liquefied natural gas, and the like.
Liquid amine absorbents, including alkanolamines, dissolved in water are probably the most common absorbents for removing acid gases. Commercially, amine scrubbing typically involves contacting the acid gas containing fluid stream with an aqueous solution of one or more simple amines (e.g., monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), triethanolamine (TEA) and its isomers, or 2-(2-aminoethoxy)ethanol (sometimes referred to as diglycolamine or DGA)) as disclosed in U.S. Pat. Nos. 4,336,233; 4,997,630; 5,877,386; and 6,337,059 and WO 2013188367. Alternatively, EP 0134948 discloses mixing an acid with select alkaline materials such as MDEA, to provide enhanced acid gas removal.
Acid gas removal from liquid natural gas streams typically takes place in liquid-liquid contacting equipment whereas acid gas removal for gaseous streams takes place in gas-liquid contacting equipment typically cyclic absorption technologies such as Pressure Swing Absorption (PSA) and Temperature Swing Absorption (TSA) using liquid absorbents. Liquid-liquid separations present unique problems not encountered with gas-liquid separations and visa versa. Loss of amine due to solubility is a particular problem in liquid-liquid separation processes, but not relevant in gas-liquid separation processes. On the other hand, loss of amine due to volatility can be a particular problem in gas-liquid separation processes while irrelevant in liquid-liquid separations. As a practical matter, amines with low solubility useful for liquid-liquid separations may not necessarily have low volatility desired for gas-liquid separations.
Typically, in gas-liquid processes, the aqueous amine solution contacts the gaseous mixture comprising the acidic gases counter currently at low temperature and high pressure in an absorber tower. Cyclic sorption processes require high rates of gas-liquid exchange, the transfer of large liquid inventories between the absorption and regeneration steps, and high energy requirements for the regeneration of amine solutions. Such processes require a large temperature differential in the gas stream between the absorption and desorption (regeneration) parts of the cycle. In conventional aqueous amine scrubbing methods relatively low temperatures, e.g., less than 50° C., are required for acid gas uptake with an increase to a temperature to above about 100° C., e.g., 120° C. or higher, required for the desorption. With the need to regenerate large quantities of solution at temperatures above 100° C., many amines commonly used in gas-liquid separation process suffer significant amine loss due to vaporization in the temperature swing processes.
While the above mentioned amine compounds are effective at removing acid gases from gas and/or liquid mixtures, they each have limitations which detract from their universal use. In particular, it would be desirable to have and aqueous amine composition with reduced loss due to volatility which is efficient at removing acid gases, in particular H2S, at a commercially viable capacity from a gaseous mixture.